How can I convert my TEI headers to CMDI?

There is no general procedure to do this, as

Text Encoding Initiative

See: http://en.wikipedia.org/wiki/Text_Encoding_Initiative

has many variants and extensions. However, you could follow the following general workflow:

• Inspect your TEI headers and decide what the relevant parts are. Some information (e.g. layout tags etc.) might be lost during the conversion.
• Compare your needs with one of the existing TEI profiles (teiHeader type 1, teiHeader type 2, teiHeader type 3) in the
  Component Metadata Infrastructure
  See: http://www.clarin.eu/cmdi
  component registry. If it fulfills your needs, go to the next steps. If it does not, use the TEI profile as a basis to create your own CMDI profile.
• Create an XSLT that generates CMDI instances (according to the profile that you chose in the previous step) from the TEI files. (Have a look at olac2cmdi.xsl and imdi2clarin.xsl for some inspiration).